Since the devil knows the Bible, does he know what the rapture means and could he be trying to rush it, slow it, or is he not concerned?
I think you’ve hit on the main reason God has chosen not to reveal the exact timing of the rapture, and why it will happen on a day no one could have predicted in advance. It’s because that way there is no possibility for Satan to develop any kind of counter strategy.
There’s nothing Satan can do about the Rapture, but that doesn’t mean he’s unconcerned. The rapture of the Church will be the most dramatic sign that his defeat is at hand since the rebirth of Israel.